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Abstract:

An evaluation device provides a transceiver system with performance
information. The transceiver system models channels between a transmitter
and a receiver thereof using Nakagami distribution with a fading
parameter. The evaluation device includes a setting module, a computing
module and an output module. The computing module is operable, based upon
the fading parameter, an average SNR of the channels, a number of
transmit antennas and a number of receive antennas, to estimate an
average output SNR, a bit error rate and an outage probability related to
signals received by the receiver. The output module is operable to
provide the transceiver system with the average SNR and the estimated
information as the performance information.

Claims:

1. An evaluation device for providing a transceiver system with
transceiving performance information thereof, the transceiver system
including a transmitter that has a plurality of transmit antennas and a
receiver that has a plurality of receive antennas for receiving signals
from the transmitter, and modeling channels between the transmitter and
the receiver using Nakagami distribution with a fading parameter, said
evaluation device comprising: a setting module operable to set an average
signal-to-noise ratio (SNR) for the channels between the transmitter and
the receiver of the transceiver system; a computing module operable,
based upon the fading parameter, the average SNR, a number of the
transmit antennas and a number of the receive antennas, to estimate at
least one of an average output SNR, a bit error rate and an outage
probability that are related to signals received by the receiver of the
transceiver system; and an output module operable to provide the
transceiver system with the average SNR and said at least one of the
average output SNR, the bit error rate and the outage probability as the
transceiving performance information of the transceiver system.

2. The evaluation device as claimed in claim 1, wherein said computing
module is operable to estimate one of the average output SNR, the bit
error rate and the outage probability by computing a finite number of
summation operations, and the number of the summation operations is
independent from the number of the receive antennas and the fading
parameter.

3. The evaluation device as claimed in claim 1, the transmit antennas of
the transmitter being assigned with respective ordinal numbers in a
specified sequence, wherein said computing module is operable, further
based upon one of the ordinal numbers of the transmit antennas, to
estimate one of the average output SNR, the bit error rate and the outage
probability that are related to signals received by the receive antennas
from a corresponding one of the transmit antennas that is assigned with
said one of the ordinal numbers.

8. The evaluation device as claimed in claim 3, wherein, when the average
SNR is greater than a predetermined value, said computing module is
operable to estimate the outage probability Pout(R, γ), which
corresponds to a given capacity R and the average SNR γ, based upon
P out ( R , γ _ ) = m mlL R [ ( m L
R ) ! ] l ( L T l ) ( λ γ _ )
mlL R ##EQU00014## where l is said one of the ordinal numbers, m is
the fading parameter, LT is the number of the transmit antennas,
LR is the number of the receive antennas, and λ=2.sup.R-1.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an evaluation device for providing
a transceiver system with performance information thereof, more
particularly to an evaluation device for providing a transceiver system,
which models a channel thereof using Nakagami distribution, with
transceiving performance information thereof.

[0003] 2. Description of the Related Art

[0004] Referring to FIG. 1, a conventional transceiver system 900 under a
transmit antenna selection/maximal-ratio combining (TAS/MRC) scheme
includes a transmitter (TX) and a receiver (RX). The
transmitter (TX) includes a modulator 91, a diversity unit 92
electrically connected to the modulator 91, and a plurality of transmit
antennas 93 electrically connected to the diversity unit 92. The receiver
(RX) includes a plurality of receive antennas 94, a synthesis unit
95 electrically connected to the receive antennas 94, and a demodulator
96 electrically connected to the synthesis unit 95.

[0005] The conventional transceiver system 900 is operable, in advance, to
estimate the channels between the transmitter (TX) and the receiver
(RX), so that the diversity unit 92 of the transmitter (TX) is
operable to select one of the transmit antennas 93, which results in a
channel that has relatively better performance, for transmitting a signal
generated by the modulator 91. Then, when the receive antennas 94 of the
receiver (RX) receive signals from the selected one of the transmit
antennas 93, the synthesis unit 95 of the receiver (RX) is operable
to weight and synthesize the signals received by the receive antennas 94.
Accordingly, performance of the conventional transceiver system 900 is
optimized, that is to say, the conventional transceiver system 900 has,
for example, a relatively greater diversity gain or a relatively greater
average signal-to-noise ratio (SNR).

[0006] However, the conventional transceiver system 900 under the TAS/MRC
scheme merely has the optimized performance for a single receiver (Rx).
When further including additional receivers (Rx), the conventional
transceiver system 900 may not be able to optimize transmission
performance between the transmitter (TX) and some of the receivers
(RX), and thus, the overall performance thereof may be decreased.

[0007] Accordingly, a transmit generalized selection/maximal-ratio
combining (TGS/MRC) scheme is provided as a solution for the
above-mentioned drawback of the conventional transceiver system 900 under
the TAS/MRC scheme. In particular, a conventional transceiver system
under the TGS/MRC scheme does not have to select one of transmit
antennas, which may result in a channel that has relatively better
performance, for transmitting signals, and can be operable to transmit
signals with a different one of the transmit antennas according to a
different situation so as to ensure the overall performance thereof and
transmission quality for various receivers.

[0008] In "Performance of Selection MIMO Systems with Generalized
Selection Criterion over Nakagami-m Fading Channels," IEICE Trans.
Commun., E89-B(12), pages 3467-3470, 2006, S. Choi and Y. C. Ko proposed
a method for evaluating performance of the conventional transceiver
system under the TGS/MRC scheme by using Nakagami channel model (see
Nakagami distribution shown in FIG. 2) to simulate the channels of the
conventional transceiver system under the TGS/MRC scheme. In this method,
an average output SNR and a bit error rate are computed for evaluating
performance of the conventional transceiver system under the TGS/MRC
scheme. However, the computational load of the average output SNR and the
bit error rate is considerably large, that is to say, a number
m×LR of summation operations are executed for obtaining the
average output SNR and the bit error rate, where m is a fading parameter
of the Nakagami distribution and LR is a number of the receiver
antennas. Further, computation of an outage probability of the
conventional transceiver system is not provided in this method.

SUMMARY OF THE INVENTION

[0009] Therefore, an object of the present invention is to provide an
evaluation device that requires fewer computations for providing a
transceiver system with transceiving performance information thereof.

[0010] Accordingly, an evaluation device of the present invention is
configured to provide a transceiver system with transceiving performance
information thereof. The transceiver system includes a transmitter having
a plurality of transmit antennas and a receiver having a plurality of
receive antennas for receiving signals from the transmitter, and models
channels between the transmitter and the receiver using Nakagami
distribution with a fading parameter. The evaluation device comprises a
setting module, a computing module and an output module.

[0011] The setting module is operable to set an average signal-to-noise
ratio (SNR) for the channels between the transmitter and the receiver of
the transceiver system. The computing module is operable, based upon the
fading parameter, the average SNR, a number of the transmit antennas and
a number of the receive antennas, to estimate at least one of an average
output SNR, a bit error rate and an outage probability that are related
to signals received by the receiver of the transceiver system. The output
module is operable to provide the transceiver system with the average SNR
and said at least one of the average output SNR, the bit error rate and
the outage probability as the transceiving performance information of the
transceiver system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Other features and advantages of the present invention will become
apparent in the following detailed description of the preferred
embodiment with reference to the accompanying drawings, of which:

[0015] FIG. 3 is a block diagram illustrating a transceiver system
provided with a preferred embodiment of an evaluation device of this
invention;

[0016]FIG. 4 is a block diagram illustrating the evaluation device of the
preferred embodiment;

[0017]FIG. 5 is a flow chart of an evaluation method implemented by the
evaluation device of this embodiment;

[0018]FIG. 6 is a simulation plot for illustrating normalized average
output signal-to-noise ratios for respective transmit antennas of the
transceiver system of the preferred embodiment with respect to fading
parameters of Nakagami channel model;

[0019]FIG. 7 is a simulation plot for illustrating normalized average
output signal-to-noise ratios for respective transmit antennas of a
conventional transceiver system with respect to the fading parameters of
the same Nakagami channel model in FIG. 6;

[0020]FIG. 8 is a simulation plot for illustrating a relationship between
a bit error rate and an average signal-to-noise ratio; and

[0021]FIG. 9 is a simulation plot for illustrating a relationship between
an outage probability and an average signal-to-noise ratio.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] Referring to FIG. 3, a transceiver system 100 under a transmit
generalized selection/maximal-ratio combining (TGS/MRC) scheme includes a
transmitter 1 and a receiver 2 coupled to the preferred embodiment of an
evaluation device 200 of this invention. For instance, the transmitter 1
is a base station, and the receiver 2 is a cell phone. The transmitter 1
includes a diversity unit 11 and a number (LT, LT>1) of
transmit antennas 12, and the receiver 2 includes a number (LR,
LR>1) of receive antennas 22, a synthesis unit 21, and a channel
estimator 23. For illustrative purposes, in FIG. 3, the transmitter 1
includes three (LT=3) of the transmit antennas 12, and the receiver
2 includes two (LR=2) of the receive antennas 22.

[0023] In such a TGS/MRC scheme, there area number (LT×LR)
of possible channels, each of which is defined by one of the transmit
antennas 12 and one of the receive antennas 22 and can be simulated using
Nakagami channel model (see Nakagami distribution shown in FIG. 2) with a
positive fading parameter (m). The channel estimator of the receiver 2 is
operable to estimate an instantaneous output signal-to-noise ratio (SNR)
of a synthesized signal generated by the synthesis unit 21 applying
maximal-ratio combining to signals received by the receive antennas 22
from each one of the transmit antennas 12, and to provide the diversity
unit 11 of the transmitter 1 with a number (LT) of the instantaneous
output SNRs corresponding respectively to the transmit antennas 12.
Accordingly, the diversity unit 11 is operable to sort the instantaneous
output SNRs in a specified sequence according to increasing magnitude,
and to assign the transmit antennas 12 with respective positive integer
ordinal numbers (l, 1≦l≦LT) according to the specified
sequence. In particular, a smaller one of the ordinal numbers (l)
indicates a corresponding one of the transmit antennas 12 with a smaller
instantaneous output SNR.

[0024] Under the TGS/MRC scheme, the diversity unit 11 is operable to
select one of the transmit antennas 12, which corresponds to one of the
ordinal numbers (l), for transmitting signals, and the channels between
the selected one of the transmit antennas 12 and the receive antennas 22
are simulated using the Nakagami channel model (see FIG. 2) and
preferably have a same average signal-to-noise ratio (SNR, γ). When
the fading parameter (m) of the Nakagami channel model and the number
(LR) of the receive antennas 22 is an integer, an average output SNR
( γ.sub.(l)), a bit error rate (PBER) and an outage
probability (Pout(R, γ)) of the synthesized signal outputted
by the synthesis unit 21 can be computed based upon the following
Equations (1) to (5).

[0025] Generally, the average output SNR ( γ.sub.(l)) can be
expressed as

for 2≦k≦(LT-l+n)(mLR-1)-1, and
βk=[(mLR-1)!].sup.-(L.sup.T.sup.-l+n) for
k=(LT-l+n)(mLR-1).

[0026] When the transceiver system 100 is configured to perform signal
modulation using binary phase-shift keying (BPSK), the bit error rate
(PBER) of the synthesized signal outputted by the synthesis unit 21
can be expressed as

[0029] It should be noted that, although the transceiver system 100 is
exemplarily illustrated as the TGS/MRC scheme, configuration thereof may
be considered as a transmit antenna selection/maximal-ratio combining
(TAS/MRC) scheme when the ordinal number (l) is equal to the number
(LT) of the transmit antennas 12. Further, the Nakagami channel
model is able to cover a wide range of fading severity due to variation
of the fading parameter (m), and includes the Rayleigh fading channel
(i.e., m=1) as a special case.

[0030] Referring to FIGS. 3 and 4, the evaluation device 200 of the
preferred embodiment is configured for analyzing the synthesized signal
from the synthesis unit 21 so as to provide the transceiver system 100
with the transceiving performance information of the transceiver system
100. The evaluation device 200 includes a setting module 3, a computing
module 4 coupled to the setting module 3, and an output module 5 coupled
to the computing module 4.

[0031] The setting module 3 is operable to set the average signal-to-noise
ratio (γ) for the possible channels between the transmitter 1 and
the receiver 2 of the transceiver system 100. Based upon one of the
ordinal numbers (l), the fading parameter (m) of Nakagami distribution,
the average SNR ( γ), the number (LT) of the transmit antennas
12, and the number (LR) of the receive antennas 22, the computing
module 4 is operable to estimate at least one of the average output SNR (
γ.sub.(l)), the bit error rate (PBER) and the outage
probability (Pout(R, γ)) of the synthesized signal according
to an appropriate one of Equations (1) to (5). Then, the output module 5
is operable to provide the transceiver system 100 with the average SNR (
γ) and said at least one of the average output SNR (
γ.sub.(l)), the bit error rate (PBER) and the outage
probability (Pout(R, γ)) as the transceiving performance
information of the transceiver system 100.

[0032] It can be appreciated that, when the computing module 4 computes
the average output SNR ( γ.sub.(l)), the bit error rate (PBER)
and the outage probability (Pout(R, γ)) with a finite number
of summation operations (Σ), i.e., Equations (1), (2) and (4), the
number of the summation operations is independent from the number
(LR) of the receive antennas 22 and the fading parameter (m) of the
Nakagami channel model. The following Table 1 shows a comparison of
computation of the performance information between this embodiment and
the method proposed by S. Choi and Y. C. Ko in "Performance of Selection
MIMO Systems with Generalized Selection Criterion over Nakagami-m Fading
Channels," IEICE Trans. Commun., E89-B (12), pages 3467-3470, 2006.

[0033] As shown in Table 1, in the method proposed by S. Choi and Y. C.
Ko, when the fading parameter (m) is equal to 1, computation of the
average output SNR ( γ.sub.(l)) and computation of the bit error
rate (PBER) both involve twelve summation operations (Σ) for
an ultra-high-speed packet transmission scheme that is proposed by NTT
DoCoMo and that includes twelve receive antennas 22 in the receiver 2 of
the transceiver system 100. Compared with the method proposed by S. Choi
and Y. C. Ko, the computation of the average output SNR (
γ.sub.(l)) and computation of the bit error rate (PBER)
performed by the computing module 4 of this embodiment are considerably
less. In addition, computation of the outage probability (Pout(R,
γ)) will not increase when the fading parameter (m) or the number
(LR) of the receive antennas 22 is increased.

[0034]FIG. 5 shows a flow chart of an evaluation method implemented by
the evaluation device 300 of this embodiment.

[0035] In step 61, the setting module 3 is operable to set each of the
possible channels with the same average SNR ( γ).

[0036] In step 62, based upon one of the ordinal numbers (l), the fading
parameter (m) of Nakagami distribution, the average SNR ( γ), the
number (LT) of the transmit antennas 12, and the number (LR) of
the receive antennas 22, the computing module 4 is operable to compute
one of the average output SNR ( γ.sub.(l)), the bit error rate
(PBER) and the outage probability (Pout(R, γ)) according
to an appropriate one of Equations (1) to (5). In particular, the
computing module 4 is operable to compute the average output SNR (
γ.sub.(l)) based upon Equation (1). When the average SNR ( γ)
is greater than the predetermined value, the computing module 4 is
operable to compute the bit error rate (PBER) and the outage
probability (Pout(R, γ)) based upon Equations (3) and (5),
respectively. Otherwise, the computing module 4 is operable to compute
the bit error rate (PBER) and the outage probability (Pout(R,
γ)) based upon Equations (2) and (4), respectively. In practice,
the computing module 4 may be configured to estimate another one of the
average output SNR ( γ.sub.(l)), the bit error rate (PBER) and
the outage probability (Pout(R, γ)) according to another one
of the ordinal numbers (l).

[0037] In step 63, the output module 5 is operable to determine whether
there is an instruction of setting another average SNR ( γ). The
flow goes back step 61 when the determination is affirmative, and goes to
step 64 when otherwise.

[0038] In step 64, the output module 5 is operable to provide the
transceiver system 100 with at least one of the average output SNR (
γ.sub.(l)), the bit error rate (PBER) and the outage
probability (Pout(R, γ)) corresponding to each of the average
SNRs ( γ) set in step 61 as the transceiving performance
information of the transceiver system 100.

[0039]FIG. 6 shows the average output SNRs ( γ.sub.(l)), which are
normalized after estimation according to Equation (1), for the respective
transmit antennas 12 (i.e., according to the respective ordinal number
(l)) with respect to fading parameters (m) of the Nakagami channel model
when the transceiver system 100 includes four transmit antennas 12
(LT=4) and four receive antennas 22 (LR=4). FIG. 7 shows the
normalized average output SNRs ( γ.sub.(l)) according to the method
proposed by S. Choi et al. under a transmission condition same as that in
FIG. 6. It can be appreciated that the simulation results shown in FIGS.
6 and 7 are almost identical, that is to say, accuracy of the average
output SNRs ( γ.sub.(l)) estimated according to Equation (1) is
substantially equal to accuracy of the average output SNRs (
γ.sub.(l)) obtained through the method proposed by S. Choi et al.
Moreover, from FIG. 6, when the channels between the transmitter 1 and
the receiver 2 are relatively stable (i.e., the fading parameters (m) are
relatively greater), the influence of the selection of the transmit
antennas 12 on the average output SNRs ( γ.sub.(l)) of the
synthesized signal is relatively less. Namely, it is unnecessary for the
diversity unit 11 to select one of the transmit antennas 12, which
corresponds to a greatest average output SNR ( γ.sub.(l)), for
transmitting signals.

[0040]FIG. 8 shows the evaluation results for the transceiver system. 100
configured for BPSK modulation. In the case of FIG. 8, the transceiver
system 100 includes four transmit antennas 12 (LT=4) and two receive
antennas 22 (LR=2), and the fading parameter (m) of Nakagami
distribution is set as 0.5. The symbols quadrature, ⋄, Δ
and ◯ represent the bit error rates (PBER) computed
according to Equation (2) when l=1 to 4, respectively, and the dashed
lines "- - - " are respective asymptotes of the bit error rates
(PBER) estimated from Equation (3). It could be appreciated from
FIG. 8 that the bit error rates (PBER) decrease as the average SNRs
( γ) increase, that is to say, transmission error of the
transceiver system 100 decreases and the performance thereof is
relatively better. Also, the bit error rates (PBER) from Equation
(3) are almost identical to the bit error rates (PBER) from Equation
(2) as the average SNRs ( γ) increase, that is to say, Equation (3)
is practical in computing the bit error rates (PBER) when the
average SNRs ( γ) are greater than a predetermined value.

[0041]FIG. 9 shows the evaluation results for the transceiver system 100,
where the transceiver system 100 includes four transmit antennas 12
(LT=4) and two receive antennas 22 (LR=2), the fading parameter
(m) of Nakagami distribution is set as 0.5, and the given capacity (R) is
2 bits/s/Hz. The symbols quadrature, ⋄, Δ and
◯ represent the outage probability (Pout(R, γ))
estimated from Equation (4) when l=1 to 4, respectively, and the dashed
lines "- - - " are respective asymptotes of the outage probability
(Pout(R, γ)) estimated from Equation (5). Similarly, it could
be appreciated from FIG. 9 that the outage probability (Pout(R,
γ)) estimated from Equation (5) is almost identical to the outage
probability (Pout(R, γ)) estimated from Equation (4) as the
average SNRs ( γ) increase. Namely, Equation (5) is practical in
computing the outage probability (Pout(R, γ)) when the average
SNR ( γ) is greater than a predetermined value.

[0042] In conclusion, the evaluation device 200 according to the present
invention is capable of computing, based upon Equations (1) to (5), the
average output SNR ( γ.sub.(l)), the bit error rate (PBER) and
the outage probability (Pout(R, γ)) of the synthesized signal
generated by the synthesis unit 21 of the transceiver system 100.
Equations (1), (2) and (4) for computing the average output SNR (
γ.sub.(l)), the bit error rate (PBER) and the outage
probability (Pout(R, γ)) are relatively simple (i.e., the
number of the summation operations (Σ) is independent from the
fading parameter (m) and the number (LR) of the receive antennas
22), and the simplified Equations (3) and (5) respectively from Equations
(2) and (4) are practical when the average SNR ( γ) is greater than
a predetermined value. Thus, computation of the average output SNR (
γ.sub.(l)), the bit error rate (PBER) and the outage
probability (Pout(R, γ)) based upon Equations (1) to (5) is
relatively less, especially for the case of a relatively large number of
the receive antennas 22 and a relatively large fading parameter (m).

[0043] While the present invention has been described in connection with
what is considered the most practical and preferred embodiment, it is
understood that this invention is not limited to the disclosed embodiment
but is intended to cover various arrangements included within the spirit
and scope of the broadest interpretation so as to encompass all such
modifications and equivalent arrangements.